1. Field of the Invention
The present invention relates to a communication network for vehicle control and a method of diagnosing the same, and more particularly, to a communication network for vehicle control which comprises a plurality of control units connected to one another via communication lines for transmitting and receiving their respective unique signals, each control unit accompanied with at least one of auxiliary input and output devices, each of at least two of the control units comprising a transmitter, a receiver, a controller, and an indicating or displaying means and provided with a diagnosis function, and a method of diagnosing the same.
2. Description of the Related Art
A communication network for vehicle control is known comprising a plurality of control units (such as ECUs) connected to one another via communication lines for mutual communications, each control unit including a transmitter, a receiver, and a controller and accompanied with auxiliary input and output devices. If any internal fault or error occurs in such a vehicle control communications network, it is identified and located by the operator performing manual checking and examining voltages and conductions in the input, output, and transmission circuits of each of the control units. This action of identifying and locating a fault or error in the relevant circuits of the control unit or its component will require the operator to have a particular skill and take a considerable length of working time, hence degrading the quality of service.
For eliminating the above problems and speeding up the detection of a fault and its location in the control unit and its relevant circuits, various improvements have been introduced in which the control unit itself is provided with a self-diagnosis function for recording and indicating the fault and its location, or a separate error diagnosis system for subsequent check up, diagnosis and/or repair is prepared and connected to the self-diagnosis function of a vehicle to be examined for reading and indicating the fault data or locations. The self-diagnosis function is commonly started by the action of timer interruption, manual interruption, or specific switching. Such conventional improvements of the self-diagnosis function for use in a vehicle mounted electronic control apparatus are disclosed in Japanese Patent Laid-open Publications SHO57-86544, SHO58-149834, SHO62-279151, and HEI6-30477.
When the control units of a vehicle control communications network are provided with such a self-diagnosis function, they may perform the diagnosing action readily and accurately but cause the overall system arrangement of the vehicle control communication network to become bulky and complicated, thus increasing the cost of production. In addition, such a separate error diagnosis system capable of connection to the known self-diagnosis apparatus has to be prepared at every local service station whereby the overall cost will be much more increased.
For example, any fault in the conventional vehicle control communication network having the control units connected to one another via communication lines and being possible to be self-diagnosed, is examined whether it derives from the communicating functions between the control units (e.g. transmission function of signals and conformity of the specification and destination from one unit to another) or the input and output control functions. The faults in the communicating functions are further classified into those of the transmitter circuit, the receiver circuit, the communication lines, and the ECU in the control unit. The faults in the input and output control functions are classified into those of the auxiliary input and output devices, the signal lines, and the control circuit in the ECU. For automatically identifying and locating the fault in a conventional self-diagnosis method, a software of greater size is hence required. Also, its relating display and indicating means are needed of elaborate and bulky types, thus increasing further the overall cost.